The ability to verify the authenticity of documents (defined broadly as any set of digitized information) in the electronic age has become more challenging at the same time as it has become more needed. Documents in electronic form are everywhere in modern banking, commerce, government, law, indeed, in modern life in general. In a world where documents are created, submitted, processed, stored, considered, etc., all electronically, sometimes even in multiple locations in the “cloud” unknown to the users themselves, notary or other official seals, physical signatures, special papers and other such tools are becoming increasingly unsuitable and unreliable.
Perhaps the most common way at present to verify the authenticity of electronic documents is to use some form of digital signature to “sign” them, which is typically accomplished using some form of asymmetric cryptography. Many different signing schemes are known that are suitable for signing both individual and sets of documents. At present, the most common data-signing methods rely on some form of the PKI (Public Key Infrastructure). A disadvantage of PKI-based digital signature schemes, however, is that the keys can be compromised; once a key is known to be compromised, any signatures created with that key can no longer be relied on. Since the likelihood that a key will become compromised increases over time, signatures created using keyed cryptography are useful mostly for a short-term purposes.
One other common method for verification involves publication, including, for example (but not necessarily) proof of an order of receipt using a sequence value bound to the digital record. When publishing is used to make a verifiable binding, the service provider typically publishes a digital record together with a sequence value in a widely-witnessed manner, for example, in a newspaper. If the service provider commits to certain rules regarding publication, then the published content can be relied upon as having been certified by the service provider. Since no cryptographic keys are used in the publication method, the problem of key compromise is not a concern. However, the publication method is inefficiently slow and unsuitable for large document collections. Publication is realistic daily or weekly, but instant certificate creation, though demanded by the modern electronic market, is impossible.
When it comes to verifying the authenticity of digital documents, regardless of whether the user cares about proof of receipt order or not, most existing methods have the serious flaw that users must in some way trust some service provider and/or clock at some point. In short, one or both of two common problems beset known authentication schemes: either there must be some “trust authority” or the systems are not amenable to extensive scalability.
Guardtime AS of Tallinn, Estonia, provides a keyless, distributed hash tree-based data signature infrastructure that it currently refers to as the Keyless Signature Infrastructure (KSI). The KSI infrastructure provides a robust and scalable verification system that does not require a trusted authority and, as its name implies, does not need to rely on keys. Although such a distributed, hash tree-based infrastructure (Guardtime's or otherwise) can verify the authenticity of a given document to a very high degree of certainty (especially Guardtime's), in many cases it may be desirable to be able to verify not only the contents of a given document, but also to identify one or more of the entities involved in the original document-registration process.